This invention relates to an improved engine control system and method and more particularly to a simplified control system and method for engines.
Feedback control systems have been proposed for use in engine management systems to improve engine performance, fuel economy and exhaust emission control. One form of feedback control system employs an air/fuel ratio sensor such as an oxygen (O.sub.2) sensor. The oxygen sensor is positioned to receive the exhaust gases from the combustion chamber. From determining the amount of oxygen in the exhaust gases the actual air/fuel ratio burnt in the cylinder can be determined.
Although oxygen sensor feedback control systems can offer the prospect of very efficient and effective engine control, they are quite costly. In addition, there are some engine conditions wherein the feedback control from a sensor such as an oxygen sensor are not possible. For example, under initial startup and until the oxygen sensor reaches its operating temperature, it cannot be utilized as a control system. Furthermore, there is a wide variety of other engine running conditions wherein the output of the O.sub.2 sensor for a variety of reasons cannot be employed for control. Even with feed back control systems the initial setting of the fuel air ratio is based on certain engine measurements and the feed back system makes adjustments in the basic settings based on the output of the O.sub.2 sensor.
Thus, for these control conditions in engines that operate basically on a feedback control system and for other engines having simpler control systems, it is desirable to provide a very effective control system and method for the engine. Various arrangements have been provided for controlling the engine to maintain the desired fuel air ratio and exhaust emission control when feedback control is not employed. Generally these systems measure engine or ambient conditions and operate from one or more maps so as to provide the desired control for the various conditions sensed. Obviously, the more conditions sensed the greater the memory and map capacity of the control unit must be. On the other hand, the simpler the system is, the more likely it is to be not fully responsive to the actual running conditions of the engine.
It is, therefore, a principal object of this invention to provide an improved control system for an engine wherein the control system is simple and also provides effective control.
It is a still further object of this invention to provide an improved and simplified control system and method for an engine that can be utilized for engines without feedback control or for engines that have feedback control, but at such times when feedback control is not feasible or desirable.
As has been previously noted, the number of conditions sensed will determine the cost of the system. The more conditions sensed, the greater number of sensors required and also the more complicated the control strategy is. Therefore, it has been proposed to provide an engine control system wherein the engine control is based primarily on engine speed and engine load. Engine speed measuring devices are relatively simple, but engine load measuring devices take a wide variety of forms. For example, the simplest form of load sensor is nothing more than a throttle position sensor. The operator throttle position is a very good indication of the operator demand and also the load on the engine. However, engine throttle position sensors are not always accurate under all conditions.
Another form of sensor which may be utilized as an indication of engine load is an air flow sensor. These sensors take a wide variety of shapes and series of operation, but for the most part they are expensive. Therefore, in a simplified system, it is desirable and maybe optimal to employ a throttle position sensor and an engine speed sensor.
As has been noted, however, the utilization of a throttle position sensor is not always reliable since these sensors may be subject to malfunction. That is, the devices are primarily mechanical and require mechanical adjustment and/or setting. These adjustments can be easily upset. On the other hand, if the use of the throttle position sensor is totally eliminated, then in most engine running conditions the engine control is not as accurate as could be desired.
It is, therefore, a principal object of this invention to provide an improved engine control system and method that operates under most circumstances on engine load and speed control utilizing a throttle position sensor, but wherein another alternative control routine is possible in the event of malfunctions in the throttle position sensor.
It is a primary object of the invention to provide an improved and simplified engine control system and method.